Decades of civil-rights law hung in the balance Wednesday as the Supreme Court heard oral arguments in a case seeking to end the federal government’s role as arbiter of states’ decisions on how to run elections, with one conservative justice saying the role perpetuated “racial entitlement.”

Conservative and liberal-leaning justices engaged in often terse back-and-forth, suggesting a 5-4 decision in a challenge to a key provision in the 1965 Voting Rights Act that requires all or parts of 16 states with a history of discrimination in voting — mostly in the South — to get federal approval before making any changes in the way they hold elections.

Justice Anthony M. Kennedy, considered the key swing vote on the case, suggested the advance approval, or “preclearance” requirement has been an effective tool in federal government’s fight against voter discrimination. But he hinted it may have outlived its usefulness, saying “times change.”

The plaintiff, Shelby County, Ala., is appealing preclearance, saying it’s no longer needed because the county and state have made significant progress in combating voter discrimination and no longer should be forced to live under extra oversight from Washington not required of other jurisdictions.

“The South has changed,” Bert Rein, an attorney representing Shelby County, told the court.

Justice Sonia Sotomayor questioned the argument, saying there is a “real record as to what Alabama has done to earn its place on the [preclearance] list.” Justice Stephen Breyer added preclearance has been effective in combating voter discrimination but that “the disease is still there in the state.”

But Mr. Rein countered that jurisdictions shouldn’t be forced to continue to pay for past voting-rights violations long-since fixed. And several conservative-leaning justices hinted they may agree.

Chief Justice John G. Roberts Jr. said that Massachusetts — a state not covered by preclearance — has the nation’s biggest black-white disparity in voter turnout and voter registration.

The chief justice then asked the attorney representing the Justice Department if it was the federal government’s opinion that Americans in the South are more racist than those in the North?

“It is not,” Solicitor General Donald Verrilli said.

Congress has reauthorized the Voting Rights Act several times, most recently for another 25 years in 2006 with broad bipartisan majorities in both chambers — including a 98-0 Senate tally.

Justice Antonin Scalia suggested Congress voted to reauthorize the law because they had nothing to gain politically by opposing it. He then suggested that preclearance represented a “perpetuation of racial entitlement” and that the Supreme Court has a duty to stop an ineffective or harmful law that Congress is unwilling to kill.

“Whenever a society adopts racial entitlements, it is very difficult to get out of them through the normal political processes,” he said.

Myrna Perez, senior counsel at the Brennan Center for Justice at the New York University Law School, predicts Justice Kennedy will side with a 5-4 majority on the nine-member court to keep preclearance intact.

“The questions that he was asking are not the kind that I believe are going to lead to a finding on unconstitutionality,” she said.